Electrical signaling system



Sept; 17, 1946. R, AYL R HAL 2,407,910

ELECTRICAL SIGNALING SYSTEM Filed June 30, 1943 INVENTOR'S REGINALDTAYLOR GEORGE moms BAKER ATTORNEY P atented Sept. 17, 1946 ELECTRICALSIGNALING SYSTEM Reginald Taylor and George Thomas Baker,

Liverpool, England, assignors, by mesne assignments, to AutomaticElectric Laboratories, Inc., Chicago, 111., a corporation of DelawareApplication June 30, 1943, Serial No. 492,832 In Great Britain August20, 1942 11 Claims. 1

The present invention relates to electrical signaling systems such asautomatic telephone systems in which trains of impulses are utilised toeffect the setting of automatic switches or the like and i particularlyconcerned with arrangements for overcoming the efiects of distortion inthe break-make ratio of impulses comprising interruptions in a normallyclosed circuit. Such distortion as is Well known is due to the efiect ofthe inductive and capacitative properties of the line on the respondingrelay and may become very serious where long lines or a number ofimpulse repetitions are involved.

The chief object of the invention is to provide a simple and reliablearrangement for correcting for the effects of distortion and enablingthe ratio of received impulses to be restored to its original or even amore desirable value.

The invention may be of particular value in connection with systemsemploying to some extent at least switches having circuit arrangementsof the type disclosed in our application S. No. 434,762 filed Mar. 14,1942. It is shown that such switches need no longer be dependent uponthe usual break to make ratio of received impulses, but rather upon theperiod which elapses between corresponding points in successive impulsesso that the only limit is that the actual speed of impulsing must not beso slow that the period between similar points in successive impulsesexceeds a predetermined amount. When such period is exceeded, aswitching operation is arranged to take place characteristic either ofthe end of an impulse train or of the release of the connectiondepending upon the final condition of the control circuit. Such a methodof impulsing is sometimes referred to as speed timing. The speed timingimpulse responding cir-.

cuit thus provides a means of response to incoming impulses whichoperates equally well no matter how badly they are degraded due to thereactive nature of the line and its terminations or to the number ofstages of impulse repetition involved.

In order that advantage can be taken of such arrangements on existingautomatic telephone networks or for interworking from networks emplOyingspeed timing selectors into ordinary networks of existing types, it isnecessary to provide means for remaking received distorted impulses sothat they can be passed on in a form acceptable to existing equipment.

One means, particularly applicable to long distance dialling, isdisclosed in our application S. No. 446,900 filed June 13, 1942, inwhich trains of distorted impulses are received on a speed timingimpulse responding circuit including an electro-mechanical impulsestorage and regenerating device, so that received impulse trains areretransmitted in a form corrected as regards ratio and at the nominalspeed for the system concerned.

Such an arrangement does more than is really necessary for satisfactoryselector operation, since it is only the impulse ratio which isdistorted during transmission, the speed of impulsing being unaffected.The present invention provides an impulse responding circuit which, inaccordance with the impulsing speed concerned, will produce a suitableoutgoing impulse ratio which will be acceptable to the receivingapparatus involved.

According to one feature of the invention, in an electrical signalingsystem employing trains of impulses comprising interruptions in a.control circuit, an impulse repeater is provided in which incomingimpulses are repeated without storage at the speed at which they arrivbut with a ratio of break to make substantially independent of thi speedand of the ratio of the incoming impulses.

According to-another feature of the invention,

in an electrical signaling system employing trains of impulsescomprising interruptions in a, control circuit, an impulse repeater isprovided in which the length of the first repeated interruption is fixedand the length of subsequent interruptions is adjusted dependent on thespeed of the incoming impulses but regardless of their ratio of break tomake.

A further feature of the invention is that in an electrical signalingsystem employing trains of impulses comprising interruptions in acontrol circuit, an impulse repeater is provided in which incomingimpulses are repeated without storage at the speed at which they arrivebut with a ratio of break to make which progressively approaches apredetermined value for successive impulses of a train.

The invention will be better understood from the following descriptionof one method of carrying it into efiect, which should be taken inconjunction with the accompanying drawing comprising Figs. 1-3. Theseall show the invention applied to an outgoing impulse repeating relayset at a tandem automatic telephone exchange, access to the relay setbeing had over one 01' more ranks of tandem selector switches operatedover a junction line from a calling automatic exchange, while the relayset itself connects with an outgoing junction from the tandem exchangeto a 3 distant automatic exchange. Fig. 1 shows the complete circuits ofthe relay set in question,

while Figs. 2 and 3 are fragments only showing alternative circuitconnections involving a socalled stabilising condenser QY whichfunctions to reduce the oscillatory nature of the output impulse ratiocontrol exerted by the circuit of Fig. 1.

Before proceeding with the detailed circuit description the principle ofoperation will be dealt with generally and it may be pointed out thatthe circuit arrangement entirely ignores the ratio of incoming impulses,and functions on the basis of their speed alone to give a suitableoutput ratio which will be acceptable to any selector in the system.

It is assumed that the telephone networks employ selector switches ofthe decimal step-by-step two-motion type employing the well-known, A, B

and C impulse responding relay triad and responsive to impulses at anominal speed of ten impulses per second and of a nominal break to makeratio of 2-1.

The switches are readily responsive to impulses having a speed range offrom 8l2 I. P. S. providing there is no serious ratio distortion, thetransmitted break and make periods over this range of speeds being asfollows,

Speed Break period Make period energised when impulsing starts have agood margin on the first impulse'and generally tend tofail only on thelast of a long train of say 9 or 10 impulses.

On the first release of the relay set impulse responding A relay, a 55m. 5. break period is deliveredin the output circuit regardless of thelength of time the A'relay stays down. After the 55 m. s. period theremainder of the first impulse is then measured, that is to say, untilthe A relay once again releases at the commencement of the break Iperiod of the second impulse, this period constituting the make periodof the first output impulse.

If this output make period is 28 m. s., thus corresponding to the 55 m.s. break which obtains at a speed of 12 I. P. S., the second outputbreak period can also be 55 m. s. with a resultant make period of 28 m.s. and these Values can remain unchanged throughout the train. If thefirst output make period exceeds 28 m. s. thereby indicating-that thespeed is of a. value less than 12 I. P. S., a suitable increase in thesecond output .break periodwill be made. The second output make periodcomprising the difference between the complete second impulse time andthe second break period will thereupon determine the length for thethird break period and so on. Similarly, in the unlikely event of themake period being less than 28 m. s., thereby indicating a speedexceeding 12 I. P. S., the second output break period will be suitablyreduced from the 55 m. s. value. The second output make period whichwill be greater than the first output make period owing to the reductionof the break period will then determine the length of the third outputbreak period and so on. In this manner the output break and make periodsare so adjusted as to give an outgoing junction to the distant automaticexchange.

, The various timing functions involved in the operation of the circuitare performed by condenser/resistance timing circuits each of whichafter a predetermined charging period builds up a suiiicient potentialacross its condenser to strike a gas discharge tube connected incircuittherewith and so to energise a relay to perform the requiredcontrolling function. The tube NTA, preferably a neon tube, andassociated condenser QX perform the timing function in connection withthe ratio replacement feature of the relay set, while neon tube NTB inassociation with condenser QW performs the speed timing function so .asto enable the appropriate circuit changes to be made at the end of eachtrain of impulses.

Preferably the neon tubes are arranged to strike at a voltage of theorder of .150 volts and this voltage is built up across the condenserswhich are connected to .the exchange battery of 50 volts by connectingin series therewith a high voltage supply HV, at a potential of 150volts, via a suitable adjustable resistance. The supply HV is shcwnseparately in various parts of the circuit as different batteries (inthe same manner as is the ordinary 50 volt exchange battery supply), andits negative pole is connected to earth so that a charging voltage of200 volts is available from the two batteries inseries.

When the relay set is taken into use, relay A operates and at contactsat brings up relay B which locks over contacts hi and at contactsbZprepares a circuit for the outgoing pulsing relay PU, at contacts 174applies guard earth to themcoming P lead, at contacts 125 connects aloop comprising the supervisory relays Dand I across the outgoingnegative and positive conductors in order to seize the distant automaticequipment, and at contacts b3 completes a charging circuit for condenserQX v'ia thepotentiometer arrangement comprising adjustable resistancesYY and YZ. The values of thes'eresistancesare suchthat condenser QX willbe charged to avoltage somewhat lower than the striking voltage of theneon tube NTA, say about volts, and the'circuit is now ready to receivetrains of impulses. 0

When relay A releases in response tothe break period of the firstimpulse received, relay PU rapidly operates, locks over contacts pul andat contacts 1M6 opens the outgoing seizing loop so as'to repeat thebreak period of the impulse to the distant automatic exchange. Atcontacts pus it completes a charging circuit for condenser QX Via thevariable resistance YX and at contacts pueit operates relay C to prepareforthe charging of the speed timing condenser QW Via variable resistanceYW and contacts 02, the charging of this condenser being prevented atpresent by the connection of the low resistance shunt thereon viacontacts pu4 and resistance YA.

Contacts zmZ connect neon tube NTA and relay E.

across condenser QX, while the remaining contacts pal are only requiredin the modifications shown in Figs. 2 and 3. Relay C in Operating, atcontacts cl disconnects the original potentiometer circuit, looks atcontacts 03 and at contacts 04 short-circuits the supervisory relays Dand I to provide an impedance-free impulse repeatin loop to the distantexchange.

On the operation of relay PU condenser QX will start charging up and itis arranged that it will reach the striking voltage of neon tube NTA in55 m. s. Tube NTA then strikes and brings up relay E which at contactsel releases relay PU regardless of whether the impulse responding relayA is still normal or not, and completes a locking circuit for itself ifrelay A is still normal. Relay PU in releasing, at contacts pu3completes a discharge path for condenser QX via resistance YZ, atcontacts Ipufi closes the loop to the distant exchange so as toterminate the break portion of the outgoing impulse and at contacts p114removes the shunt from across condense QW so as to initiate the chargingof this condenser. Relay C, it will be seen, remains looked overcontacts er2 and 03 independently of relay PU and further considerationof the operation of the speed timing circuit for controlling relay C andinvolving tube NTB and condenser QW will be deferred until the operationof the ratio replacement circuit has been completed.

As previously mentioned, relay PU in restoring at contacts pu3 completesa discharge circuit for condenser QX,'while at contacts 1W2 it opens theoperating circuit for relay E. The latter relay is maintained operatedfor so long as relay A remains normal over contacts cl, b2 and al andthis arrangement ensures that relay PU hall not re-operate until thenext release of relay A.

The voltage to which condenser QX discharges is dependent on the timerelay PU is normal, i. e. until the beginning of the break period of thesecond received impulse at which time relay PU is re-operated, and atcontacts p143 reconnects condenser QX up to the charging circuit viaresistance YX. If this released period of relay PU, which determines themake period of the first outgoing impulse, is just the correct length tocorrespond to a 55 m. s. break, i. e. if it is no longer than the 28 m.5. make period which obtains at 12 LP. S., it is arranged that condenserQX will have discharged to the same value, namely 100 volts, as at thecommencement of the first break. Hence the second output break will alsobe 55 m. s. with a resultant make of 28 m. s. as determined by thedifierence between the complete impulse length of 83 m. s. and theoutput break period of 55 m. s. and these values will remain unchangedthroughout the train.

If, therefore, impulses are received at a speed of 12 I. P. S.,thenregardless of their ratio they are repeated with a replaced break tomake ratio of 2-1 (55 m. s. break, 28 m. s. make) corresponding to thenominal 2-1 ratio at which they were transmitted at the distant sendingend, and which is most suitable for the satisfactory operation of thedistant automatic exchange selectors.

If the length of time relay PU is released exceeds 28 m. 5., therebyindicating that the length of the complete impulse is greater than 83 m.s. and hence that the impulsing speed is less than 12 I. P. S.,condenser QX when discharged via resistance YZ will drop below itsoriginal voltage of 100 volts and the time required for charging it upagain to the tube striking voltage of 150 volts will therefore begreater so that the break.

period of the nextiimpulse will be lengthened.

In the unlikely event of the released period ofrelay PU being too shortto correspond to a 55 satisfactory operation of the selector switches.It should be mentioned that in some circum-.v

stances it may not be essential to maintain in the output the nominal2-1 break to make ratio at all impulsing speeds as in order to securethe most satisfactory operation of the selector switches it may bedesirable to effect slight alterations in the outgoing ratio over thespeed range.

Considering now the operation of the speed timing circuit involvingcondenser QW and tube NTB, this functions by determining whether theactual length'of each impulse is greater or less 1 than a fixedpredetermined period which is approximately equal to the length of thelongest impulse which can be tolerated, namely, a 143 m. s. impulsewhich corresponds to the minimum dial speed of 7 I. P. S.

If the predetermined value is exceeded without a further impulsearriving, it is an indication either that the impulse train has finishedor that the calling party has hung up prematurely. In the former casethe timing circuit on coming into operation and bringing up relay ERreleases relay C at contact e72 and re-introduces the supervisory relays.D and I across the outgoing leads at contacts 6T3, while in the lattercase since the A relay will be normal, relay B will also be released atcontacts erl and will restore the relay set to normal.

If impulses follow one another within the predetermined time period, thenext impulse will reset the timing device by discharging condenserQW'and the timing operation will recommence. This re-setting operationis repeated for each impulse of a train until the last impulse of thetrain has been received when the tube NTB is able to strike and operaterelay ER as described above.

In the arrangement described in the previously mentioned specificationNo. 434,762 the timing circuit is adapted to effect a switchingoperation after 143 m. s. measured from the beginning of the breakperiod of the first impulse of a train (neglecting the magnet operatingtime), the arrangements being that it will be reset if a succeedingbreak is received within thi 143 m. s. period. In the present instance,instead of using one 143 m. s. timing circuit to compare the periodextending between, say, the beginning of one break period to the samepoint in the next, it

the minimum speed of impulsing of 7 I. P. S.

NTB in a time not less than 88 m. s. so as to provide an overall timingperiod of 143 m. s. In the case of an impulse train at any impulsingspeed above the minimum of '7 I. P. S.,- relay PU will operate toinitiate the break period of the next impulse before the lapse of 143 m.s. from its first operation and hence condenser QW will be dischargedwithout the tube striking. At the end of the second output break periodas determined by the impulsing speed concerned, relay PU in releasingwill initiate the timing of a second 88 m. s. period and so on until theend of the impulse train.

At the end of the train relay PU will fail to re-operate and condenserQW will therefore reach the striking voltage of tube NTB 88 m. s. afterthe end of the last output break period and tube NTB will flash and willbring up relay ER. Relay ER in operating opens the locking circuit ofrelay 0, and at contacts er3 connects resistance YBacros the outgoingspeaking conductors. On release of relay C the supervisory relays D andI in parallel with resistance YB are introduced across the outgoingspeaking conductors, resistance YB serving to obviate any danger ofrelease of the distant battery feeding relay due to the initial highimpedance of the supervisory relays. When the voltage on condenser QWfalls below the holding voltage of tube NTB, this tube will de-ioniseand relay ER will commence to release slowly. On the release of relayER, resistance YB is disconnected from the outgoing speaking conductors.

Further received impulse trains are dealt with as before described andafter the last train has been received the relay set functions in knownmanner, relay D which is polarised by rectifiers MBA and MR3 serving toextend the called partys supervision signals back to the calling side ofthe circuit by reversing the connections of relay A tothe speakingconductors.

If the subscriber should hang up during dialling, a break simulating animpulse will be received so that when relay E operates after thecondenser QX charging period relay PU will be released and relay E willremain locked to the earthed back contacts al so that relay PU cannot bere-operated. 88 m. s. after the release of relay PU tube NTB will flashto bring up relay ER which as before opens the locking circuit ofrelayC. In this instance however since the A relay is not now operated,and since the alternative holding circuit for relay B is opened bycontacts erl, relay B will now release and will release relay E andinitiate release of the connection.

Returning again to the ratio replacement timing circuit, since the 55 m.s. fixed first output break period corresponds to the break period of a12 I. P. S. break impulse at the nominal 2-1 break/make ratio, and sinceit is desirable that at a speed of 12 I. P. S. the output impulses shallhave this ratio to secure the most satisfactory operation of theselectors, it follows that if the resultant first output make period is28 m. s. corresponding to an i'mpulsing speed of 12 I. P. S. it isnecessary to make condenser QX discharge from 150 volts to say 100 voltsin 28 m. s. thus providing a 55 m. second break 'period and so on asdescribed;

If however, the received impulses are at a speed of say I. P; 6., thefirst output make 8 period will be m. sand condenser'QX will dischargetoa value lower than 100 volts. 7 If the 2-1 break/make output ratio isalso to be mailtained'at this speed, the next charging time re- 7 quiredby condenser QX to reach the tube NTA striking value must then be 66% m.s. to produce the appropriate second output break period for 10 I. P. S.Under this condition condenser QX will subsequently only have 33 m. s.discharge time during the second output make period. It will then reacha voltage somewhere between the 100 volt Value and the value to which itdischarged in the 45 m. first make, and clearly the third chargingperiodwill not therefore be as great as 66 m. -s. so that the thirdoutput break period will lie somewhere between and 66 /3 m. s. and soon.

The correction afforded bythe scheme as shown in Fig. 1 is thusoscillatory in nature and is particularly marked if the maximumcorrection is placed on the second output impulse as above described byway of example. The introduction of condenser QY into the ratioreplacement circuit in the manner shown in Fig. 2 is found to produce amarked stabilisation eilect with the result that the outgoing impulseratio settles down to the calculated suitable value almost immediately.

Referring now to Fig. 2, it will be. seen that condenser QY is initiallycharged up to the same 100-volt value as condenser QX. When relay PUoperates to connect condenser QX to the charging circuit at contactspu3, the circuit for condenser QY is disconnected at contacts 10141.When condenser QX is to be discharged after having flashed the tube NTAand having brought up relay E, with the resultant release of relay PU,it initially rapidly shares out its 150 volt striking voltage with thevolt charge on condenser QY and both condensers then proceed to discharge via resistance YZ. On the next operation of relay PU in responseto the next release of relay A,the discharge of both condensers isterminated and condenser QX commences to re-charge' When condenser QX isto be discharged, it will initially share out its volt charge withwhatever charge has remained on condenser QY after the last dischargeand both condensers will then proceed to discharge throughresistanceYZ'as before. Similar remarks apply to each succeeding impulseof the train.

The best relative values of condenser QY and QX can be determined bycalculation of the condenser charge and discharge times and voltagesunder simple conditions and such calculation shows the markedimprovement which can be effected by the'introduction of the stabilisingcondenser. 7

An alternative method of stabilising is shown in Fig. 3 where it will beseen that before condenser QX proceeds to discharge via resistance YZit'shares out its striking voltage of 150 volts with whatever voltagecondenser QY has accumulated via variable resistance YV during thechargingtime of condenser QX.

It' should be pointed out that the .'ratio' replacement circuit iscompletely independent of incoming junction resistance values so that itis unnecessary for the circuit to be associated with any particularjunction line. Moreover, since it entirely ignores the ratio of theincoming impulses it will function to give the desired output as long asany impulses are received, no matter how badly they are degraded,provided relay .A

relay PU and opens it sufficiently long to release relay E.

What we claim as new and desire to secure by Letters Patent is:

1. In a signaling system, a repeater responsive to received make andbreak impulses over an incoming circuit for repeating the same over anoutgoing circuit, a relay in the repeater operated by the firstinterruption of the incoming circuit, a second relay responsive to theoperation of the first relay to open the outgoing circuit, a condenser,a gas discharge tube, means for charging the condenser to the strikingvoltage of the tube, and means responsive to the striking of the tube toterminate the operation of the second relay and thereby close theoutgoing circuit.

2. In a signaling system, an impulse repeater controlled over anincoming circuit by break and make impulses to repeat similar impulsesin an outgoing circuit, a relay in said repeater responsive to a breakin the incoming circuit, a second relay operated by the first relay tocontrol the outgoing circuit, a condenser, a gas discharge tube, saidcondenser connected in a charging circuit by the operation of saidsecond relay and continuing to charge until it reaches the strikingvoltage of said tube, and means operated when the tube strikes forcausing restoration of the second relay.

3. A system as claimed in claim 2 in which said second relay closes adischarge circuit for said condenser for a time dependent on the nextinterruption of said incoming circuit, the amount of dischargecontrolling the time of operation of said second relay upon its nextenergization.

4. In an impulse repeater, a line relay responsive to received impulsesconsisting of breaks and makes of an incoming circuit, an outgoingcircuit, a relay controlled by the line relay for opening the outgoingcircuit when the line relay is deenergized, a condenser having apreliminary charge and connected for an additional charge by said secondrelay to time the break of the outgoing circuit, means for dischargingsaid condenser to different points responsive to subsequent receivedimpulses to thereby determine the time of break of the outgoing circuitupon the next operation of said second relay.

5. A system as claimed in claim 2 including a second condenser and a gasdischarge tube for timing the released time of said second relay, andmeans for terminating impulsing conditions if said second relay isreleased for more than a predetermined time.

6. In an impulse repeater, a line relay responsive to received break andmake impulses, a second relay controlled by each deenergization of theline relay to repeat a break impulse,-a condenser and a gas dischargetube for timing the break of each repeated impulse in accordance withthe time between received break impulses, and a second condenser and asecond gas discharge tube for preventing further operations in case thetime between received break impulses exceeds a predetermined time.

7. In a signaling system, an impulse repeater having an input circuitover which impulsesof varying speed and break to make ratio arereceived, relay means in said repeater responsive to said receivedimpulses for repeating corresponding impulses over an output circuitwithout storage and at the same speed as received, and timing meanscomprising an aperiodic circuit and a gaseous discharge tube associatedwith said relay means for causing the break to make ratio of therepeated impulses to have a desired value which is substantiallyindependent of the speed or ratio of the received impulses.

8. In a signaling system, an impulse repeater having an input circuitover which impulses of varying speed and break to make ratio arereceived, relay means in said repeater responsive to said receivedimpulses for repeating corresponding impulses over an output circuitwithout storage and at the same speed as received, and timing meansassociated with said relay means for causing the first repeated breakimpulse to have a fixed length and for varying the length ofsubsequently repeated break impulses in accordance with the speed of thereceived impulses.

9. In a signaling system, an impulse repeater, a circuit over whichimpulses of varying speed and break to make ratio are at times received,relay means in said repeater responsive to said received impulses forrepeating corresponding impulses over a further circuit without storageand at the same speed as received, a first timing means associated withsaid relay means for causing the break to make ratio of the repeatedimpulses to have a desired value which is substantially independent ofthe speed or ratio of the received impulses, and a second timing meansassociated with said relay means for terminating impulsing conditions apredetermined time interval after the last impulse of a series.

10. A signaling system as claimed in claim 9 in which each of saidtiming means comprises an aperiodic circuit and a gaseous dischargetube.

11. In a signaling system, a first circuit over which impulses are attimes transmitted, a gas discharge tube, means associated with saidfirst circuit for initiating an impulse over a further circuit and forinitiating the flow of an aperiodic current in a circuit connected tosaid tube in response to the receipt of an impulse over said firstcircuit, said aperiodic current causing the tube to fire a predeterminedtime interval thereafter, and said means being operated when said tubefires to terminate the impulse over said further circuit.

REGINALD TAYLOR. GEORGE THOMAS BAKER.

